package 跳台阶;

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    static int N = 50;
    static int[] f = new int[N];

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        f[1] = 1;
        f[2] = 2;
        for (int i = 3; i <= n; i++) {
            f[i] = f[i - 1] + f[i - 2];
        }
        System.out.println(f[n]);
    }
}
